The p-i-n photodiode has been found extremely useful as an optical to electrical energy transducer. The p-i-n photodiode generally consists of a layer of p-type conductivity material formed over a layer of intrinsic, or i-type material, formed over a layer of n-type conductivity material. In operation, radiation to be detected is absorbed in the i-layer where it generates electron-hole pairs. These pairs are separated by an electric biasing field resulting in current flow to an external circuit as carriers drift across the intrinsic region to the p and n regions and are collected by metallic contacts.
A planar or lateral form of p-i-n photodiode is described in U.S. Pat. No. 4,282,541. In this device, a pair of spaced apart, elongaged p- and n-type mesas are formed on an intrinsic or semi-insulating single crystal body by molecular beam epitaxial growth. In the planar p-i-n photodiode, the i-region between the p and n mesas is directly exposed to incident radiation, thus enabling efficiently photogeneration of electron-hole pairs, which are then able to drift and/or diffuse to the p- and n-type mesas.
Planar p-i-n photodiodes are generally formed by conventional semiconductor processes, such as molecular beam epitaxy (MBE) or diffusion or ion-implantation processes, each of which has distinct disadvantages. MBE requires ultra-high vacuum equipment, and diffusion and ion-implantation involve relatively high temperature processes. Additionally, each of these processes require a separate step of forming a contact on the p- and n-type surfaces for collecting the photogenerated electrons. This step, again, usually requires subjecting the detector body to high temperatures with the resultant possibility of damaging the previously formed body.
Accordingly, a need exists for a simple, low cost process for forming p-i-n lateral photodetectors which does not require relatively high temperatures or high vacuum.